Influenza is a globally important pathogen responsible for intermittent lethal pandemics. Present vaccination strategies are mainly based on a trivalent vaccine created prior to each season to reflect the strains predicted to be circulating that season. However, the need to reformulate the vaccine each year has led to searches for universal influenza vaccines. The highly conserved matrix protein, M2, is a promising candidate. Although it does not prevent infection, it significantly reduces morbidity, mortality, and viral shedding in preclinical studies. It mediates protection, which can be passively transferred from vaccinated to naive animals, by the induction of specific antibodies which inhibit viral production. Conservation of the extracellular portion of M2 is striking, with over 90% of all sequenced influenzas infecting humans differing from the proposed vaccine sequence by one amino acid or less. Only the M2 proteins of the H5N1 influenza strains infecting humans show greater divergence, with three or more amino acids differing from the vaccine strain. The overall goal of this proposal is to generate a human or humanized monoclonal antibody (mAb) candidate that would be suitable for influenza therapy or passive immunization. The mAb would recognize the M2 proteins of the common circulating influenzas and H5N1 strains infecting humans, and show efficacy in murine and non-human primate influenza models. As antibodies have long in vivo half lives they can confer months of protection: long enough to cover a flu season, or the 6-8 week community duration of a pandemic. This goal will be undertaken using a number of different methods: 1) Humanization and affinity / epitope maturation of a well defined anti-M2 murine mAb; 2) Immunization and challenge of non-human primates with M2 antigens; 3) Generation of a panel of anti-M2 antibodies; 4) In vitro testing of scFvs; 5) Conversion of selected scFvs to full length antibodies; 6) Testing of full length antibodies in murine and non-human primate models. If funded, this research will provide additional measures to treat and protect against seasonal and pandemic influenza. The antibodies developed will be usable as adjunct therapy for infected individuals, as well as a passive vaccine to protect unvaccinated or inadequately vaccinated populations. As a passive vaccine, these antibodies are likely to additionally provide population protection, as a consequence of a reduction in viral shedding and consequent infectivity in treated individuals.